Photoelectric velocity detector



Jan. 3, 1939. 1 T. scHTLEBEN '2,142,378

PHOTOELECTRI CA AVELO() ITY DETECTOR Filed Dec. 25, 1936 Picafoe f ffy@ :inventor Bg y ' Gttorneg Patented Jan. 3, 1939 PHGTOELECTRIC VELGCITY DETECTOR Lawrence T. Sachtleben, Camden, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 23, 1936, Serial No. 117,296

(Cl. Z50-41.5)

4 Claims.

My invention relatesto velocity detectors and more particularly to a photo-electric means for indicating the velocity of moving bodies and including means for balancing out ordinary changes in light, as distinguished from the light reflected from moving bodies to the photo-electric means.

I am aware of the use of photo-electric devices for detecting the presence of a translucent body.

embodiment of the light-intercepting screens employed in Fig. 1, and

Figures 3A, 3B, 4A and 4B are elevational views indicating modified forms of screens.

Referring to Fig. l, a moving body is indicated by the arrow l. Light reflected from any suitable source is reflected from the arrow and traverses a path 3 indicated by dash lines 3. This light passes through objective lens 5 to create images if; In such installations, a source of light is aron the screens 9 and Il. 'Ihe mirror 1 is half lo ranged to shine on a photo-electric tube. If a silvered, so that half of the light goes through translucent body is interposed between the light the mirror and half of the light is reilected from and the photo-electric tube, the tube response is the mirror, as indicated by the dash lines 3. The indicated as a change in electric current, which two screens 9 and Il are interposed between the lo may be amplied to actuate relays, meters, or the mirror l and condensing lenses I3, I5, which are lf; like. Since the photo-electric tube has an output held within suitable housings Il, I9, and prefercurrent which varies as a function of the light ably arranged to focus images of the objective applied to the tube, it should be apparent that lens 5 on the sensitive surface of photo-electric normal variations of the light impinging on the tubes 2|, 23. These housings also support these 20 tube will aiect the output currents along with photo-electric tubes 2l, 23. 20 variation caused by intercepting a particular 'I'he electrodes of the photo-electric tubes are ci connected as follows: The plate electrodes 25, My invention contemplates applying light to 21 are connected to the primary terminals of a a, pair 0f photo-electric tubes in Such a manner transformer 29. The remaining eleCtIOdeS 3l, 33 25 that ordinary Variations of surrounding light will are COnneCted tOgether and t0 the DOSitiVe termi- 25 have substantially no eiect upon the combined nal of a battery 35. The negative terminal of output currents of the tubes, but iight reflected this battery is Connected tothe center-tap 0f the from moving bodies will be indicated as a change primary of the transformer 29. The secondary in ph0t0e1ectric Output Current-g of the transformer 29 is connected to a suitable 3U The principal object of my invention is to proamplier 3l, WhOSe Output may be applied, 30 vide an improved means for indicating the velocthrough a lter 33, t0 a reCOI'Cler 0r any Suitable ity of moving bodies. type of frequency-indicating meter 39.

Another object of my invention is to provide The Screens 9, ll are preferably made With an means for arranging a pair of photo-electric Opaque Portion @l and a transparent POrtOn 43. 3? tubes so that their normal output currents are The tl'anSlOarent lOOItOn preferably has a SinuS- 35 arranged in opposite phases, while the variation Gda form. The transparent Openings 43 are of output current as a function of light reected Preferably arranged 130 Out 0f DhaSe With refrom a moving Object is in phase spect to each other. This out of phase arrange A further Object of my invention is to provide ment allows one of the screens to admit the maxii a pair of photo-electric tubes with a pair of light mum amount of hght to lts assqciated photo' 40 intercepting screens which are arranged in opelctmc type when the 0therof Sami Screen ad' posite phase, whereby light from a moving body gst' llglllgwunt of hght to lts assoclated 4- etltsfCeggo fe s The operation of the foregoing device is esseni tially as follows: Normal variations of surround- 45 A further Obiect 1s to provlde means fm" mgl' ing light, such as the variations between the catlflg and recorfmg the Veloclty 0f movmg maximum amount of sunlight and nightfall, afbodles as a function 0f the frequency 0f Photo' fect each of the photo-electric tubes equally. electric Currents generated by the intereepten Such equal variation of current is cancelled out 5c 0f light l"eflete from the rnOVing bOdY- in the primary winding of the transformer 29 50 My inVentiOn may be leest underStOOC by l'efel'- and, therefore, has no effect on the recorder 39. ence to the accompanying drawing in which If an object, such as the arrow l, is moving across Figure lis a schematic circuit arrangement of the field of the objective lens 5, its image will one embodiment of my invention, move on the screens 9 and I I, being divided into 5,53 Figures 2A and 2B are elevational views of one two identical images by the mirror l. As the 55 image of the arrow moves across the intercepting screens in the direction indicated by arrows 45, lil, variable amounts of light'will be imposed on the photo-electric tubes. This variation is at a maximum in tube 2i at the same time that it is at a minimum with respect to tube 23. These opposing effects establish currents which add up in the transformer primary 29 and are further amplified and finally recorded on the meter 39. Since the rate of change of photo-electric currents depends solely on the rate at which the image of the moving object is intercepted by the screen openings, the output frequency will be a direct function or the velocity of the moving body. 'Ihe lter 38 may be adjusted to pass frequencies above or below desired limits, or may be omitted from the circuit.

It should be understood that my invention may be applied to devices for recording the velocity of moving automobiles, airplanes, trains, pedestrians, and the like. For example, my invention may be placed above a highway, so that vehicles passing under the lens 5 would operate the recorder to either w'sibly indicate the frequency of the photo-electric currents, actuate an alarm at velocities exceeding predetermined limits, or record on a moving tape suitable symbols Which could be transcribed in terms of velocity.

I do not limit my invention to any particular type of meter or recorder. It should be understood that suitable types of frequency meters and suitable types of recorders are commercially available. While I prefer to use screens with sinusoidal light admitting portions, my invention is not limited to any particular screen opening. 'Ihe screen openings may be made successively smaller or arranged to admit successively smaller amounts of light, as shown respectively in Figs. 3A, 3B and Figs. 4A, 4B, to vary the amplitude, as wellY as the frequency, of the photo-electric currents and thereby indicate the direction of movement and the velocity of a moving body. Likewise, while a 180 relationship is specified between the screen openings, other angular displacements may be used.

I claim as my invention:

l. The method of indicating the velocity of a moving body which comprises dividing light from said body into two paths, alternately passing light in iirst one and then the other of said paths,

gradually reducing the amount of light passing along a portion of said paths, creating electric currents by the light alternately passing said paths, said currents diminishing as a function of said gradual reduction of light, and indicating the frequency of said currents and the diminu- 2. In a device for indicating the velocity and n direction of a moving object, means for obtaining a plurality of light images of said object, light responsive devices each positioned to respond to one of said light images, a plurality of screens including a plurality of apertures, one screen positioned between each of said light images and its respective light responsive device for alternately transmitting and rejecting said light images as they move across said screen; said apertures being of variable area and constant length along a line parallel to the movement of said image, whereby the motion of said body causes said light image falling upon said light sensitive device through said screen to be interrupted by said screen to produce output currents whose changing amplitude is a measure of the direction of said motion, and whose frequency is proportional to the speed of said object.

3. In a device for indicating the direction and velocity of a moving object, means for producing a plurality'of similar images of said object, a separate opaque screen for receiving each of said images, each screen including a plurality of transparent apertures, said apertures being of varying area and constant length, said screens being so positioned that when said image falls on an aperture o1 one screen the corresponding image falls upon an opaque portion of the other screen, a photoelectric device arranged to receive the light transmitted through each screen, whereby the frequency of the output currents of said devices indicates the speed of said object and the change in the amplitude of said currents indicates its direction of travel.

4. In a device for indicating the direction and velocity of a moving object, means for producing a plurality of similar images of said object, a separate opaque screen for receiving each of said images, each screen including a plurality of apertures of uniform area and varying degree of transparency, said screens being so positioned that when said image falls on an aperture of one screen the corresponding image falls upon an opaque portion of the other screen, a photoelectric device arranged to receive the light transmitted through each screen, whereby the frequency of the output currents of said devices indicates the speed of said object and the change in the amplitude of said currents indicates its direction of travel.

LAWRENCE T. SACHTLEBEN. 

